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bringing it home
By windspeed, Section Wind Posted on Sun Jul 13th, 2008 at 12:53:44 PM MST
how much is too much

I have a 24 v dual rotor flying it averages 25 kwh per week
my batteries are 70 yards from my house
I assume the losses would be to high at 24 v
I would like to start and run a 2.5 kw motor for maybe 3 hrs per day
looking for a basic (cheap) inverter 230- 240 v would 3kwh be suitable
also what size battery bank would do
any ideas please
windspeed

bringing it home | 10 comments (10 topical, 0 editorial)

Re: bringing it home (3.00 / 0) (#1)
by wpowokal on Sun Jul 13th, 2008 at 07:32:13 AM MST
(User Info)

What amp/hour batteries do you have?

Do you have a cable 70 yard long or are you seking info on that point?

Cheep inverters or more precisley those relying on switchmode as opposed to those with a torridal transformer have inherent poor surge capabilities.

A 2.5 Kw motor? What is it driving, ie what starting load does it have? NO a cheep 3Kw inverter will NOT start it.

A 2.5 Kw motor for 3 hours /day is 52.5Kw plus starting, you need more incomming power.

What size battery bank? I hope someone else can tell you but for me there is insuficient information/hard facts.

Please don't be discouraged by my response, but.......... your post lacks genuine info....... it's a bit like I have a piece of string... how long is it?

For me your given information does not stack up, hopefully others will prove me stipid and answer your post.

allan down under
A life lived in fear is a life half lived.

Re: bringing it home (3.00 / 0) (#2)
by windspeed on Sun Jul 13th, 2008 at 08:58:40 AM MST
(User Info)

Thanks wpowokal
I have not bought the cable yet ...info appreciated
yes I understand I would need sufficient surge
the motor will be pumping refrigerant should not be excessive load
I have the option of mains power when my batteries drop
at the moment I have 600 ah just a starting point
I am not discouraged by your response .. you have give me a chance to develope my question in the right way

thanks ..windspeed

[ Parent ]

Re: bringing it home (3.00 / 0) (#3)
by wpowokal on Sun Jul 13th, 2008 at 09:11:11 AM MST
(User Info)

So a long coupled refer unit, that's about as hard a load to start as you get, make that a 12.5 Kw inverter to start it. (5 times running load).

Much better to have any inverter at the batteries and transmitt the 240V power.

Are your two 5Kw inverters stackable like Outback units? Also please note Outback units have atrocious surge capabilities, in my opinion. Goes to 70 yard cable size.

OK on batteries just remember to not let them discharge too far or they will die a premature death.

You will not start a motor of that size, under load with cheep inverters.

Keep posting and someone will get to cable size.

allan down under
A life lived in fear is a life half lived.
[ Parent ]

Re: bringing it home (3.00 / 0) (#4)
by windspeed on Mon Jul 14th, 2008 at 03:25:50 PM MST
(User Info)

"So a long coupled refer unit, that's about as hard a load to start as you get,"
do you mean the 70 yards of cable is doubling the starting load for the motor
I intend to have the inverter at the batteries and using 10 sq mm (8 awg )to the house would you still be talking 12.5 kw
I have not bought any inverter yet, but they should have low voltage disconnect
maybe not so cheap..........
thanks again....windspeed

[ Parent ]

Re: bringing it home (3.00 / 0) (#5)
by wpowokal on Mon Jul 14th, 2008 at 05:40:56 PM MST
(User Info)

By long coupled I meant "V" belt coupled, just my asumption, but any refridgeration is a hard load to start. That is why one allows 5 time running current for starting, so yes it would stil require 12.5 Kw.

The 70 yards is not the reason, 10mm Sq will handle the load @ 240V.

As an example I run a coolroom off a 3Kw inverter that has a 9Kw surge capability, now my refer unit draws 25amps@240v to start, 5 to run (4 amps/Kw @ 240V). Now the inverter starts the unit as long as there is no other load above a few hundred watts on the inverter at the time of starting.

Your proposed load is large for Re, there are inverters that will load share with a generator or grid but in your opening post you say "cheep inverter". As I don't know why you are choosing this load off Re when you have mains I am lost to advise further.

allan down under
A life lived in fear is a life half lived.
[ Parent ]

Re: bringing it home (3.00 / 0) (#6)
by la7qz on Mon Jul 14th, 2008 at 10:59:55 PM MST
(User Info) http://home.no.net/naomij

Allan down under wrote:
"By long coupled I meant "V" belt coupled, just my asumption, but any refridgeration is a hard load to start. That is why one allows 5 time running current for starting, so yes it would stil require 12.5 Kw."

Or a softstarter or variable frequency drive which would be one helluva lot cheaper.

Owen
If you're not living on the edge, you're taking up too much space.
[ Parent ]

Re: bringing it home (3.00 / 0) (#8)
by windspeed on Tue Jul 15th, 2008 at 04:07:47 PM MST
(User Info)

the reason I am asking about starting a 2.5 kw motor is I am considering buying a air to water heating system (supposed to give 4 kw of heat for 1 kw of electricity )
could I start it on mains and switch over to inverter
thanks windspeed

[ Parent ]

Re: bringing it home (3.00 / 0) (#9)
by wpowokal on Wed Jul 16th, 2008 at 03:19:04 AM MST
(User Info)

A suitably rated two pole break before make change over switch will do it if flicked over quickly.

allan
A life lived in fear is a life half lived.
[ Parent ]

Re: bringing it home (3.00 / 0) (#7)
by bob g on Mon Jul 14th, 2008 at 11:08:39 PM MST
(User Info)

use a belt driven compressor and a centrifugal clutch off an old washing machine
to mount to your motor, that way the motor is allowed to get up to the run winding
before the clutch engages.

much lower starting amperage that way :)

or use an automotive compressor with its clutch and allow the motor to start before engaging the clutch on the compressor.

much lower starting current for the motor, but you spend a few amps for the electric clutch.

just a couple of alternatives if you hadn't considered them.

fwiw,,,probably not more than you paid for it.

bob g

Re: bringing it home (3.00 / 0) (#10)
by tanner0441 on Wed Jul 16th, 2008 at 05:22:58 PM MST
(User Info)

Hi.

If you want to know how much voltage will be left at the end of 70 yard run use the formular... Volts drop = cable resistance in ohms X max current X length in meters. All over 1000

Cable resistance per mtre can be obtained from electrical engineering manuals.

bringing it home | 10 comments (10 topical, 0 editorial)

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